380 PHYSIOLOGY CHAP. 



contains 22'6 vols. per cent of oxygen (at C. and 760 mm. Hg), 

 34'3 per cent of carbonic acid, and 1/8 per cent of nitrogen. 



According to an analysis of Setschenow, human arterial blood 

 contains 21-6 vols. per cent oxygen, 40*3 per cent carbonic acid, 

 1/5 per cent nitrogen. Some analyses of the blood of herbivores 

 (sheep, rabbit) made by Sczelkow and Walter give 10'7-13'2 

 vols. per cent oxygen, 34-45 per cent carbonic acid, 1/8-2-1 per 

 cent nitrogen. 



The gas content of venous blood is more variable, according to 

 analysis, since it depends on the circulatory velocity and activity 

 of metabolism in the several tissues traversed. At present we 

 have only analyses of the blood of the right heart, in which the 

 reduced venous blood from the whole aortic capillary system meets 

 and mingles. On the 'average of numerous analyses given in the 

 tables of Zuntz, the venous blood of the dog contains 7*15 vols. 

 per cent oxygen less than the arterial blood, 8 '2 vols. per cent 

 more carbonic acid, and much the same quantity of nitrogen, as 

 arterial blood. 



After asphyxia pushed so far as to kill the animal, the oxygen 

 does not disappear from the whole of the blood, while the carbonic 

 acid increases considerably. From a number of analyses of 

 asphyxial blood made by Setschenow, Holmgren and others, it 

 appears to contain 0'96 vols. per cent oxygen and 49 '53 per 

 cent carbonic acid : i.e. there is a deficit of 17'3 vols. per cent 

 oxygen and 1043 per cent excess carbonic acid, as compared with 

 normal arterial blood, according to the values obtained by the said 

 authors. 



Method of Extracting Gases from the Blood. The various forms of 

 apparatus adopted, after Magnus, for the mechanical extraction of gases from 

 the blood, are those of Hoppe-Seyler, Ludwig, Lothar Meyer, A. Schmidt, 

 Pfliiger, etc. They are all based essentially upon the Torricellian vacuum, 

 and aim at liberating the gases dissolved in the fluids or held in loose 

 combination. The most perfect form for the rapid and complete extraction 

 of gases is that of Pfliiger, as represented in Fig. 167. 



It consists of three principal parts : the bulb A which receives the 

 'blood direct from the artery or vein ; the tube for absorption of the water 

 vapour to dry the extracted gases B ; the mercury pump CD for aspiration 

 and the reverse, i.e. production of the Torricellian vacuum, and expulsion of 

 the gases extracted into the eudiometer tube for analysis. 



The details of construction of the apparatus are so plain on the diagram 

 that a minute description is superfluous. 



The bulb G is first connected with the tube H by turning the 3-way tap 

 G. The vessel D is then raised by the handle , so that the whole of bulb 

 (7, with which D communicates by means of the strong rubber band Fand 

 the glass tube E, is filled with mercury. When G is full, communication 

 with H is closed by a quarter turn of the tap G, and opened to the tube 

 connected with the desiccating apparatus , and also with the double bulb A, 

 after opening the tap P. The vacuum is then started in the apparatus by 

 lowering the vessel D by means of the handle , on which all the mercury 

 passes from G into D, and air rushes in from A and B to G. The tap 



